A theory of magnetization dynamics in ferrimagnetic materials with antiparallel aligned spin sub-lattices under action of spin-transfer torques (STT) is developed. We consider magnetization dynamics in GdFeCo layers in two cases of magnetic anisotropy: easy plane and easy axis. We demonstrate that, (i) for the easy plane anisotropy the precession of the N\'{e}el vector is conical and the cone angle depends on the STT strength and the value of spin non-compensation, while the frequency of precession can reach sub-THz frequencies; (ii) for the easy axis anisotropy two regimes are possible: deterministic switching of the net magnetization and a conical sub-THz precession depending on the STT strength.
@article{arxiv.1904.09341,
title = {Sub-terahertz ferrimagnetic spin-transfer torque oscillator},
author = {Ivan Lisenkov and Roman Khymyn and Johan Akerman and Nian X. Sun and Boris A. Ivanov},
journal= {arXiv preprint arXiv:1904.09341},
year = {2019}
}